Just saw this on macrumors and tried it on my ipod app, seems to work.
Prior to iPhone OS 3.0 beta, pressing and holding the home button would force quit an application. This would also free up memory from Apple's background-capable applications like Safari and Mail.
Well, this method to force quit no longer works.
To force quit an application in 3.0, press and hold the sleep/wake button until the slide to power off screen appears, then press and hold the home button until the application quits (about six seconds).
The question is, what does Apple have planned for pressing and holding the home button in the final version on 3.0?